fix(config): preserve persisted and runtime state on save failure

tests/test_config_persistence_safety.py

@@ -0,0 +1,121 @@
+import copy
+import os
+import stat
+from concurrent.futures import ThreadPoolExecutor
+from threading import Event
+from unittest.mock import Mock
+
+import pytest
+import yaml
+
+from repeater.config_manager import ConfigManager
+
+
+@pytest.mark.parametrize("failure", ["dump", "fsync", "replace"])
+def test_failed_update_preserves_file_and_shared_config(tmp_path, monkeypatch, failure):
+    path = tmp_path / "config.yaml"
+    config = {"repeater": {"node_name": "before"}, "radio_type": "pymc_tcp"}
+    before = copy.deepcopy(config)
+    path.write_text(yaml.safe_dump(config))
+    original = path.read_bytes()
+    section = config["repeater"]
+    manager = ConfigManager(str(path), config)
+    live = Mock()
+    monkeypatch.setattr(manager, "live_update_daemon", live)
+
+    def fail(*args, **kwargs):
+        if failure == "dump":
+            args[1].write("partial: ")
+        assert config == before
+        raise OSError("synthetic write failure")
+
+    target = "yaml.safe_dump" if failure == "dump" else f"os.{failure}"
+    monkeypatch.setattr(f"repeater.config_manager.{target}", fail)
+    result = manager.update_and_save({"repeater": {"node_name": "after"}})
+    assert result["success"] is False
+    assert result["saved"] is False
+    assert result["live_updated"] is False
+    assert config == before
+    assert config["repeater"] is section
+    assert path.read_bytes() == original
+    assert list(tmp_path.iterdir()) == [path]
+    live.assert_not_called()
+
+
+def test_failed_direct_save_does_not_normalize_shared_config(tmp_path, monkeypatch):
+    config = {"radio_type": "pymc_tcp", "pymc_tcp": {"host": "synthetic"}}
+    before = copy.deepcopy(config)
+    path = tmp_path / "config.yaml"
+    path.write_text(yaml.safe_dump(config))
+    original = path.read_bytes()
+    monkeypatch.setattr("repeater.config_manager.yaml.safe_dump", Mock(side_effect=OSError()))
+    assert not ConfigManager(str(path), config).save_to_file()
+    assert config == before
+    assert path.read_bytes() == original
+    assert list(tmp_path.iterdir()) == [path]
+
+
+@pytest.mark.parametrize("mode", [None, 0o600, 0o640])
+def test_atomic_save_permissions_and_publication(tmp_path, monkeypatch, mode):
+    path = tmp_path / "config.yaml"
+    config = {"repeater": {"node_name": "before", "other": 1}}
+    section = config["repeater"]
+    if mode is not None:
+        path.write_text(yaml.safe_dump(config))
+        path.chmod(mode)
+    replace = os.replace
+    observed = []
+
+    def checked_replace(source, destination):
+        assert config["repeater"]["node_name"] == "before"
+        assert stat.S_IMODE(os.stat(source).st_mode) == (mode or 0o600)
+        assert os.stat(source).st_uid == os.getuid()
+        observed.append(True)
+        replace(source, destination)
+
+    monkeypatch.setattr("repeater.config_manager.os.replace", checked_replace)
+    assert ConfigManager(str(path), config).update_and_save(
+        {"repeater": {"node_name": "after"}}, live_update=False
+    )["saved"]
+    assert observed == [True]
+    assert config["repeater"] is section
+    assert yaml.safe_load(path.read_text()) == config
+    assert stat.S_IMODE(path.stat().st_mode) == (mode or 0o600)
+    assert list(tmp_path.iterdir()) == [path]
+
+
+def test_concurrent_managers_serialize_staging_and_saving(tmp_path, monkeypatch):
+    path = tmp_path / "config.yaml"
+    config = {"repeater": {"node_name": "before"}}
+    first = ConfigManager(str(path), config)
+    second = ConfigManager(str(path), config)
+    entered, release, second_started, second_dump = Event(), Event(), Event(), Event()
+    dump = yaml.safe_dump
+
+    def paused_dump(data, *args, **kwargs):
+        if data["repeater"].get("first") and not data["repeater"].get("second"):
+            entered.set()
+            assert release.wait(5)
+        else:
+            second_dump.set()
+        return dump(data, *args, **kwargs)
+
+    def second_update():
+        second_started.set()
+        return second.update_and_save({"repeater": {"second": True}}, live_update=False)
+
+    monkeypatch.setattr("repeater.config_manager.yaml.safe_dump", paused_dump)
+    with ThreadPoolExecutor(max_workers=2) as pool:
+        a = pool.submit(first.update_and_save, {"repeater": {"first": True}}, False)
+        try:
+            assert entered.wait(5)
+            b = pool.submit(second_update)
+            assert second_started.wait(5)
+            assert not second_dump.wait(0.1)
+            assert config == {"repeater": {"node_name": "before"}}
+        finally:
+            release.set()
+        assert a.result()["saved"]
+        assert b.result()["saved"]
+    assert config["repeater"] == {"node_name": "before", "first": True, "second": True}
+    assert yaml.safe_load(path.read_text()) == config